The change of pitch or variable setting of blades of a turbine engine propeller is one way for improving the performance and output of turbine engines under different flight conditions.
It is known turbine engine such as turboprops, for example with pairs of despun propellers, referred to by the expressions “open rotor” and “unducted fan”, equipped with these pitch change systems are known. Turboprops differ from turbojet engines by the use of a propeller outside the nacelle (unducted) instead of a fan. The pitch change system may also apply to a turboprop with a propeller or adapt indifferently to several propellers.
In a turboprop of the open rotor type, a gas-generating part and a propulsion part are aligned and arranged in a stationary cylindrical nacelle supported by the structure of the aircraft. The gas-generating part can be arranged upstream or downstream from the propulsion part. The terms “upstream” and “downstream” are defined relative to the circulation of the gases in the turbine engine. The propulsion part includes a pair of coaxial and despun propellers, upstream and downstream, respectively, that are rotated in opposite directions relative to one another by a turbine, in particular a low-pressure turbine, of the gas-generating part via a reduction gear, for example an epicyclic gear set. The propellers extend substantially radially across from the transmission shaft with a longitudinal axis to the outside the nacelle. In general, each propeller comprises a substantially cylindrical rotary case bearing an outer polygonal hub received rotatably around the longitudinal axis in the stationary nacelle. The hub includes radial cylindrical housings distributed on its periphery around the longitudinal axis. Shafts with radial axes, perpendicular to the longitudinal axis of the turbine engine, secured to roots of the blades, are received in the housings of the polygonal rings and also traverse radial passages of the cylindrical case. Rotational guide bearings housed in these radial passages keep the radial shafts in their passages.
An example system for changing the pitch of each propeller is known from document WO2013/050704. In FIG. 2, this pitch change system 23A is installed in the core of the rotary parts, for example with an annular control cylinder 25A rotating the roots of the blades. The annular control cylinder 25A includes a cylinder 27A mounted on a stationary case 13A and a piston 29A connected to a connecting mechanism 26A that is connected to each shaft 47A having a radial axis. A cylindrical rotary case 11A rotates around the stationary case. To that end, at least one bearing 12A is arranged between the stationary case 13A and the rotary case 11A. The system further comprises a load transfer bearing 34A whereof the inner ring is secured to the piston 29A and the outer ring is connected to the connecting mechanism 26A and lubricating means for said bearing 34A. The movement of the piston following the fluid command of the annular control cylinder 25A ensures the desired angular pivoting of the blades by the connecting mechanism 26A by pivoting the radial shafts 47A connected to the blades. The radial shafts 47A convert the force generated by the annular control cylinder 25A into a torque directly on the module of the propeller. These shafts 47A traverse the rotating parts, on the same occasion traverse at least one ventilation duct 22A, a primary air duct 20A in which hot air circulates and a lubricant oil enclosure 23A in which the oil that made it possible to lubricate the load transfer bearing 34A propagates, under the effect of the rotation thereof, in the form of mist or droplets of oil. This oil enclosure 23A is situated near the primary air ducts 20A and zones with a high temperature gradient.
Sealing problems may arise at the passage of the radial shaft due to the forces applied on the rotary part and, in particular, the movements of the radial shafts during the movement of the pitch change system of the blades. These forces are multiplied when the control cylinder is such that it plays a structural role. The radial shafts 47A can thus move radially and axially in the rotary part.
It is therefore known, as shown in FIG. 3, to use annular sealing means 10A between the radial shaft 47A and a peripheral edge 35A of the passage of the rotary case 11A to limit, or even avoid, the risks of pollution or oil leakage. However, some sealing means are not effective, since they do not accept the radial movements of the radial shaft. Thus, the ventilation duct 22A, traversed by the radial shaft 47A, can be polluted due to the oil stored in the oil enclosure 23A and able to penetrate the ventilation duct due to the movements of the radial shaft. The sealing means 10A can also break, causing oil leaks that may lead to a fire in the turbine engine, in light of the substantial heat of this environment. It is also known to use an oil deflector 11A in case of failure of the sealing means. However, the integration of the deflector on the radial shaft in such a cluttered zone is problematic in terms of the disassembly of the radial shaft, since this would involve using the oil deflector to remove the rotational guide bearings 15A of the radial shaft or the destruction of the deflector.